Not so very long ago, a woman was lying in bed with her husband and talking. Somehow she didn't notice that he was transcribing her monologue; he recognised the tragicomic potential of her stream of anxious thoughts. When he handed over his notebook, she snorted with laughter, but also felt chastened. Seeing her thoughts written down in black and white gave her a jolt. What kind of loon was she?

She was me, and I still have the transcript.

My worries that evening covered the following topics: my hair (frizzy, split ends, more grey showing), whether the front door was locked, my eyes (possibility of an eye infection, which could preclude wearing contact lenses, which is to say: disaster), having flat feet (no good with flip-flops, so summer is effectively useless to me), was the front door really locked, the possibility of falling downstairs, my friend Sophie (why she hadn't returned my phone calls). Oh, and are you positive you locked the front door, or should I check?

Worrying is something I've always excelled at. In this subject, I'm top of the class, straight As. But it's near impossible for me to get my friends to take my angst seriously. 'Your worries are frankly too ludicrous,' said my friend Eleanor when I called her to talk about this article.

It's true. I accept many of my concerns seem unserious. And in public I make light of them, happily casting myself as a kind of female Woody Allen. But when I'm at home those ridiculous concerns can take over.

I jump from one to the next without allowing myself a moment's rest. 'As soon as you finish one worry,' says my husband, 'which you usually insist is the worst you've ever had, you immediately start on another.'

I'm not a flamboyant worrier; I don't have panic attacks, I don't wail or hyperventilate. Instead, I retreat into my own brain often for hours at a time, stuck either in the past, wishing that something that has happened hadn't (or vice versa), or in the future, overwhelmed by some monstrous circumstance that may never come to be. To my husband, this feels like I'm 'mentally absent'. It's exhausting living inside my head sometimes. It's a hideous waste of time and extremely annoying for those around me.

In my last job, on a glossy magazine, the beauty editor encouraged me to have Botox not because I was looking older (though, now I think of it, I worry that this may have been what she was hinting at), but because I looked so anxious all the time. 'I think it'll really change the way people respond to you,' she said brightly.

Did people truly think I looked worried? Now I was really worried. But I declined the Botox, because it would have done nothing to address the underlying problem.

Anxiety is a bigger problem than this navel-gazing might suggest. Across a spectrum that includes panic attacks, obsessive-compulsive disorder, post-traumatic stress, phobias and the catch-all, generalised anxiety disorder - anxiety disorder has become the most prevalent mental health problem in the world, according to a World Mental Health Survey of 18 countries.

And it's about to get worse. We are entering a new age of anxiety. As the economic situation worsens, so fretting in the general population rises. In the past year, oil prices have risen by 50 per cent, basic foods such as rice have soared by as much as 70 per cent and house prices are plummeting at a faster rate than we've seen in a long time. Those in the know are starting to whisper that we're heading for the mother of all recessions.

Most people will take little comfort in the fact that the man in charge of all this, Prime Minister Gordon Brown, bites his fingernails.

Merryn Somerset Webb, editor of MoneyWeek, has noticed clear signs of anxiety among her readers. 'People are anxious, and they are right to be. They're worrying about investments and pensions, the effect of inflation on their future, about which banks are safe and which might go bust. We have had letters from people who have lost a lot of money on the property market. People under 40 are not used to losing jobs or being made redundant. We are not used to property prices falling or not having what we want. As adults we haven't suffered hardship. I do think a lot of people are in for a big shock.'

Economists tell us that what happens in the US will happen to us nine months later. Well, in June it emerged that the American middle classes are losing their homes and finding themselves obliged to live instead in their cars, in specially designated parking lots.

City health clinics have reported a huge rise in calls from professionals facing redundancy. A helpline used by London's major banks and financial firms received 3,500 calls in June from people with anxiety and depression - a 10 per cent rise on last year. Project director James Slater says: 'People are worried about redundancies and a potential recession, which adds to people's anxiety, can tip them over the edge.'

Don Serratt, a former merchant banker and founder of the Life Works community rehab clinic, has seen a 20 per cent rise since last November in admissions related to economic anxiety. 'We are getting more and more calls from people not just in the City but professionals from all over. Things are bad right now.'

Dr Richard Bowskill, consultant psychiatrist at the Priory, is more specific: 'For a while, we have seen people worrying about mortgages and the cost of living. But now we have started to see people worrying about job security. That has a knock-on effect. It leads to people pushing themselves at work. I saw someone this morning who said they couldn't take any more time off work because they felt under scrutiny.

'The mind is just another part of the body,' Bowskill explains. 'It's an organ that normally functions well but, if put under too much strain, it starts not functioning properly. The physical symptoms are things like palpitations, stomach churning and sleep disturbance.'

Fretting and hand-wringing represent a considerable drain on our time and energy. 'People who worry a lot are generally less effective than those who don't; they get less work done and are often less happy,' says Gary Marcus, professor of psychology at New York University. In experimental tasks, worriers are slower to respond than non-worriers, presumably because worrying burns off mental energy that would be more effectively applied elsewhere. 'Worry, it has been said, is often like a rocking chair: it gives you something to do, but it doesn't necessarily get you anywhere. Evolution may have given us the opportunity to worry, but that doesn't mean we should take the bait.'

Indeed, constant worry has a clear and scientifically proven link to ill health. Chronic worriers, for example, are more likely than others to suffer from heart conditions. The connection between worry and poor health can also take a less predictable form. Two years ago, I convinced myself I had an eye infection. So I took myself to Moorfields Eye Hospital for checks. It turned out that my eye was perfectly healthy, but sitting in the casualty department among genuine patients, their eyes weeping pus, I picked up an extremely serious viral conjunctivitis that lasted three months and threatened to compromise my sight forever. The lesson: hypochondria really gave me something to worry about.

But it seems I've not got it as bad as many others. In the course of researching this story, I bought (and immediately hid inside my bag) a book called Overcoming Anxiety for Dummies. My husband flicked through it before me, and announced with some satisfaction that I didn't seem to have such a bad case after all. For instance I have never felt, like one poor unfortunate in the book, that I was actually going to die during a panic attack.

Anxiety, says psychologist Oliver James, is worrying about things you can't do anything about, or which don't matter. It's not the same as fear: fear sharpens the senses, anxiety paralyses them. 'The key thing,' James tells me, 'is that anxiety is irrational. It's a loss of priority - a lost sense of what is important and what isn't.'

In my own case, though I am concerned about the environment and the ongoing economic downturn, these are not the things that get me in a funk. I am much less likely to wake in the night in a panic about rising sea levels, or rising fuel bills, than about having a bad haircut.

Another way to look at anxiety is as a chemically induced response to threat: the hormone cortisol is secreted, in turn leading to an excess of adrenaline. You go into the fight or the flight mode. 'If your cortisol levels are permanently jammed on high,' explains James, 'you are going to feel permanently under threat. You become indiscriminate about what constitutes a threat. You go to the kitchen to make a cup of tea and worry about running out of tea bags. You become irritable, you swear, you burst into tears. You have very extreme reactions relative to the significance.'

The Michelin-starred chef Tom Aikens knows a bit about this. He's well known for an alleged incident with a palette knife that got him fired from his first restaurant. In recent years, he says, he has calmed down a lot thanks to therapy and regular exercise, but at the time - a decade ago - he was 'wound up, stressed', and liable to get upset about silly things. 'I used to bottle everything up and then explode, go off on one. It was always about the little details, because it's the little details that make food special. I would be so stupid. I would be so stressed by an overcooked piece of meat. What's the point? Just put another one on.'

According to James, a person's cortisol levels are pretty much set in the first six years of life. If he's right, I can't imagine what might have set my own levels high. I did, years ago, visit a Freudian therapist who gave me a box of hankies and encouraged me to churn up what seemed even to me to be rather petty resentments from the distant past. Rightly or wrongly, I found this approach unhelpful and didn't return. Much more helpful were sessions, a few years later, with a cognitive therapist - who tried to address the way I look at the world and respond to events - though, as must already be clear, she didn't eliminate my problems over the long term.

Rather than look back, what matters is whether I am likely to pass on my worrying tendencies to my daughter, now four years old. Although sunny, confident and happy, she has already started registering dissatisfaction with her hair (she has fabulous blonde curls) perhaps because she's witnessed too many of my frizzy-hair freak-outs. I caught her the other day staring into the mirror and stretching out one of her glorious ringlets. Is she destined to be a worrier? Can I stop that? Or will everything I do make it more likely?

There's no doubt I've become more anxious since becoming a mother. My fear of falling down stairs only started after my daughter was born; I tortured myself with thoughts of slipping while carrying my precious bundle. My hypochondria also intensified, and I became scared of swimming in the sea (I put these down to the post-natal realisation that another human really depends on me to remain alive, and healthy).

But these protective concerns can themselves produce negative effects. In spring last year, after Madeleine McCann disappeared, I became deeply anxious about my daughter's safety and let her come into our bed at night. I liked having her next to me, just to hear her breathing, and knowing she was all right. The result: she developed a fear of sleeping in her own room and it took us most of the autumn to coax her back into her own bed.

The American author and academic Katie Roiphe recognises high levels of anxiety in herself and believes that passing it on to Violet, her six-year-old daughter, is inevitable. 'I think it's impossible not to pass along that temperament,' she says. 'When I was a child I was afraid of the wind - even when I was six months old, I was that afraid of the universe. It's impossible that I should get a calm child. I look at some children who are unflappable and think that would be nice for my daughter, but I don't think it's going to happen. My daughter worries about a million things: that if she is going to drink from someone else's straw she will turn into that person. She has supernatural worries.'

But can anxiety really be explained entirely by the influence of neurotic parents, or high levels of cortisol laid down in childhood? The sudden, recent increase in anxiety among adults stressing about climate change and economic collapse suggests not. Could it be caused by consumerism, which we grow into more slowly?

It could, says Tom Hodgkinson, editor of The Idler and author of the inspirational How to Be Free. He believes that our economic system functions precisely by keeping us anxious. We're encouraged to believe, at all times, that we're just one purchase away from happiness: 'Anxious people make good consumers and good workers. Anxiety will drive us back into our comfort blankets of credit-card shopping and bad food - the system deliberately produces anxiety while simultaneously promising to take it away.'

The writer and professional worrier William Leith agrees. He breaks off from writing a new book, Bits of Me are Falling Apart, to elaborate: 'Gordon Brown is always telling us that our economy has to grow, otherwise we will fall apart. What does that mean? It means that everyone has to make you buy stuff all the time. And the way they do this is by constantly advertising. Advertising is about making you feel anxious: you're too fat, or you need a new kitchen. We live in a world where you can be playing golf and, on finally putting the ball, you find inside the hole an ad for a car. You walk away thinking, "I should buy a Lexus."'

Oliver James makes a similar case in his book Affluenza. And if we're anxious in the good times, economic downturn will be so much worse. Since the advent of the credit crunch, he argues, significant numbers of people will have been 'shitting themselves'. Their cortisol levels, he contends, will be through the ceiling. 'They will be worrying themselves silly and will become physically ill. They might start showing OCD (obsessive compulsive disorder) symptoms, trying to create something safe out of this very dangerous situation. They might think: "If I say 100 Hail Marys before leaving the house at least there is something I can do."'

If that's what they're doing, I can sympathise. At times of particular stress (or, as my husband would tell you, every night), I find myself compelled to check the front door several times. I also have a little routine for checking the cooker is turned off. I blame my husband for this: he has occasionally forgotten to turn off the gas, and if he's cavalier about the cooker then how can I be sure about the front door? But I daresay that James would point to other, deeper reasons for my obsessive checking.

Leith believes that obsessive compulsive behaviour masks deeper anxieties. 'If I am worried about a big thing like, "I'm a complete failure, half my life has gone and I'm going to be dead soon", the incidental worries get worse. If I'm sitting at my desk to start writing, I might think, "Oh, God, I can't write, I just can't do it, I just can't do it. Oh, God." At those times, I might need to check the cooker in case the house is burning down.'

Despite holding consumerism responsible, James believes that therapy can help. He particularly recommends something called the Hoffman Process, which he himself has undergone. But this seems to involve whacking cushions and pretending they are your parents, and to me it sounds horribly like the Freudian analyst I saw years ago - but worse, and more expensive.

Hodgkinson, more appealingly, encourages us to take matters into our own hands and simply shed the burden - 'the dreadful, gnawing, stomach-churning sense that things are awry, mixed with a chronic sense of powerlessness ... forever hoping, fearing or regretting'.

In How to Be Free, Hodgkinson sets out a comprehensive list of methods to encompass this liberation. These include gardening, ceasing to read newspapers or watch telly, and embracing a fatalistic theology. 'Catholics are probably less anxious than Protestants,' Hodgkinson argues. 'Buddhists are certainly less anxious than Jews.'

My husband has similar ideas. He frequently urges me to read the works of Thich Nhat Hanh, a Vietnamese Buddhist monk and best-selling self-help master. Once in a while, I give it a go. The general thrust seems to be that we should learn to live in the moment, by for instance concentrating on our breath. 'Mindful breathing helps us stop being preoccupied by sorrows of the past and anxieties of the future,' Nhat Hanh writes in one book. 'It helps us be in touch with life in the present moment.'

But worry creeps up on us even when we're counting our breaths and living in the moment. It's Leith, typically downbeat, who points this out to me. It happens, for instance, when he's negotiating pedestrian crossings with his three-year-old son: 'Before you cross,' he says, 'you wait for the green man. But what if there's no traffic coming? Should I stick to my guns and wait? Or should I cross the road? If so, surely he will realise that this is an exception? But then again, I want him to understand it has to turn green before he even thinks of crossing. I don't want him to think there's an either/or. Am I being over-anxious? There may be an appropriate level of anxiety, but no one knows what it is.'